The All-or-Nothing Bomb Test That Built a Better Bunker-Buster

Fourteen years ago, out in the scrublands of the Nevada desert on the Tonopah Test Range, a forklift slowly raised a new instrument of death onto its test stand. Built in only a few months (for reasons that remain classified) the lone missile had one chance. Success or failure, this explosive test would decide the future of the bunker-buster and teams of people who came together to make it.

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The Air Force hadtasked John Andersen of Sandia National Laboratories with this job. The challenge: build an explosive charge with enough power to break through at least 15 feet of solid rock. The design: a so-called shaped charge, a hollow cone of explosive lined with metal meant to blast a huge hole. The follow-on warhead would continue through that hole to destroy any bunker hiding below.

"It wasn't our objective to create the largest conical shaped charge ever," Andersen told Popular Mechanics. "But it happened as a result."

Normally, projects like these could take several years to complete—Andersen and his team had six months.

Normally, projects like these could take several years to get through all the design, testing, and approval phases of making a 21st-century weapon. Not this time. "We took the fast, higher risk path because no development work could be conducted," Andersen says. "The rush was part of the excitement."

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How to Make a Bunker Buster

The shaped charge, the main ingredient behind any bunker buster, is not a new idea. Anti-tank weapons all the way back to World War II have used similar designs on a much smaller scale. TheM1A1 Bazooka, for example, could make a hole the size of a pencil through three inches of steel. But the Sandia project had to supersize that hole to nine inches across and fifteen-feet deep, and it needed to pierce volcanic rock calledtuff, which Andersen compares to high-strength concrete.

A shaped charge has two main elements, the explosive and a thin metal liner, which blasts into a high-speed drill when it detonates. Because a denser explosive makes for a better shaped charge, warhead designer Manny Vigil's wanted to useHMX, an advanced explosive which can be pressed to achieve maximum density. But the cost to make such a dense charge was too expensive. Instead the team settled on Octol, an explosive which is shaped by casting rather than machining. Only three sites in the country were able to precision-cast the huge six-hundred-pound charge, and only one of these, American Ordnance in Middletown, Iowa, was willing to attempt the job on such a strict deadline.

Meanwhile, Andersen turned his attention to the metal liner, another element that would also require compromise. More elaborate designs, Andersen says, would improve penetration, but there was no time to develop and validate these advanced techniques. After all, they only had one shot. So the team chose a well-proven cone shape instead.

Usually, shaped-charge liners are not much bigger than DVDs...this liner was about the size of a manhole cover.

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The material used for the metal liner is just as important as its design. The liner needs to be as dense as possible so it can dig deep into rock. The list possible elements started with well-known dense metals like gold, platinum, and tungsten, but Andersen knew these would be too pricey. Tungsten, while not incredibly expensive is incredibly hard, so fabricating anything out of tungsten can cost upwards of $60,000.

The only possible answer was copper. Although only half as dense as tungsten, copper is cheap, easy to work with, and has been the material of choice for anti-tank charges for decades.

Usually, shaped-charge liners are not much bigger than DVDs. But for the monstrous size of this project, this liner was about the size of a manhole cover, weighing in at 117 pounds. Detailed computer modeling predicted that the charge should work without any problems. But as any engineer can tell you, computer models can fail.

All or Nothing

With all the pieces in place, the charge was assembled and fitted with a detonator and test instrumentation. The entire process of fabrication had been completed in five weeks, leaving just enough time to plan and execute the test if everything went right.

Explosive designer Manny Vigil (left) and project lead John Andersen take one last picture with the shaped charge prior to detonator installation.

Sandia National Laboratories

Andersen had confidence in the team's work, but things like surrounding wildlife, and especially weather, were beyond his control. After all, the shaped charge was out in the open and on top of a large metal frame. It was chilly, Andersen recalls, and storm clouds threatened overhead. When the lightning warnings arrived, the whole apparatus had to move into a storage bunker.

"If we had a lightning strike, that would have been a bad day," says Andersen. The safe distance from the explosive was 3,000 feet—the team evacuated two miles just to be safe.

Despite the assurance of simulations and talented engineers, everyone wondered if this missile could pull it off.

"I was still nervous before the detonation," says Andersen, with full confidence that the charge would go off but nervous that the hole wouldn't be big enough. "You've done all the preparation you can, now you see if it paid off. That's the feeling I had – confident but nervous."

Then the firing officer pressed the button and—boom.

The team returned to the test sit with fragments of the test stand and other metal scrap scattered 1,400 feet from the explosion.

The hole left by the team's new bunker buster.

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But what had happened at Ground Zero? Before they could find out, the team waited while rock fragments were vacuumed from the hole. Then they measured the hole's depth: ten inches wide while punching through 19-foot-deep hole of solid rock. Andersen's confidence prevailed:

"The test was a complete success."

Building Better Bunker Busters

After making sure a warhead could fit down this hole, the new dual-warhead design was validated. Although the Air Force did not build the bunker busting cruise missile that Andersen's nail-bitting project was designed for (though classified it was possibly in preparation for armed conflict after 9/11), its test data helped pave the way for a new generation of weapons.

This type of bunker buster can be found on the U.S. Navy'sAGM-154C Joint Standoff Weapon and theStorm Shadow used by Britain's RAF. They allow a relatively small missile to break through rock and concrete that would otherwise need the kinetic energy of a massive bomb. In June, Storm Shadows fired by RAF jetsdestroyed a large ISIS bunker in western Iraq.

Andersen went on to work on the W80 nuclear warhead and some ICBM warheads. Meanwhile work continues on shaped charges at Sandia and other National Laboratories though much of this information remains classified.

But few of them are likely to have quite as much impact as what could literally and figuratively be called a groundbreaking piece of research.

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